URBN Professor of Biomedical Innovation Drexel University, United States
Introduction: There are currently no cures for idiopathic pulmonary fibrosis (IPF). The only available treatments are two FDA-approved anti-fibrotic drugs (pirfenidone and nintedanib), which can only slow the progression of fibrosis but are associated with significant side effects or lung transplantation requiring lifelong immunosuppression. Thus, there is a major need for a therapy that can reverse established fibrosis to improve lung function and extend lifespan. Macrophages are one of the only cell types capable of remodeling fibrotic tissue into functional tissue. Therefore, macrophage cell therapy is a promising approach and holds the potential to become a functional treatment for reversing established pulmonary fibrosis. However, macrophages are highly plastic cells that rapidly shift phenotype in response to microenvironmental cues. Thus, a strategy is needed to control their phenotype in situ following administration to prevent them from changing phenotype in response to pro-inflammatory and pro-fibrotic cues at the site of injury. To achieve this and overcome the limitations of conventional macrophage cell therapy, we advanced the strategy of biomaterial-enabled intracellular control of macrophages using microparticles encapsulated with the anti-fibrotic, anti-inflammatory drug dexamethasone (Dex). Previous experiments showed that Dex-MP macrophages exhibited an anti-inflammatory, anti-fibrotic phenotype capable of withstanding additional environmental stimuli and increased phagocytosis and collagen degradation in vitro.
Materials and
Methods: To test the efficacy of biomaterial-mediated macrophage cell therapy a mouse model of progressive pulmonary fibrosis was used where fibrosis was induced by 3 doses of Bleomycin (1U/kg) given biweekly over 4 weeks. After the last Bleomycin dose, animals were housed for 6 weeks to reach the state of progressive fibrosis. GFP-positive Macrophages were loaded with Dex-loaded PLGA microparticles (MPs) (1-3 µm) in vitro before these were intratracheally administered to mice with established progressive pulmonary fibrosis. As a control, mice were treated with PBS or macrophages without MPs, macrophages with blank MP or free Dex MPs. The phenotype of administered macrophages (GFP+) and host lung macrophages (CD45+/F480+/GFP-) was analyzed via flow cytometry. Cytokine levels in the bronchial fluid were determined via ELISA, and changes in the lung collagen content after treatment administration were measured using a hydroxyproline assay.
Results, Conclusions, and Discussions: Host macrophages in the pulmonary fibrosis model increased the expression of CD163, CD206, CD301, Mertk and CD86, markers previously identified as drivers of fibrosis. Dex-MP-loaded macrophages decreased the expression of these markers in vivo compared to unloaded and blank MP-loaded macrophages. Furthermore, treatment of Dex-MP-loaded macrophages also significantly reduced the expression of these markers in host macrophages compared to untreated animals after seven days. Administering unloaded macrophages and free Dex MPs did not affect host macrophage phenotype. However, blank MP-loaded macrophages slightly reduced the expression but not to the extent of Dex-MP macrophages. Furthermore, treatment with Dex-MP-macrophages resulted in changes in the cytokine level of TGFB1 in the bronchial fluid. Moreover, treatment with Dex-MP-macrophages significantly reduced collagen content compared to untreated animals and animals treated with free Dex MPs. Interestingly, macrophages loaded with blank MP also slightly reduced the collagen content in fibrotic lungs, opening new directions in exploring how microparticles alone can be used to modulate macrophages for macrophage cell therapy.
In conclusion, these results highlight that biomaterial-enabled intracellular control of macrophages for cell therapy is a promising strategy as it shows potential for phenotype maintenance and host cell control as well as therapeutic efficacy in a model of progressive pulmonary fibrosis. Furthermore, this approach allows the induction of a complex phenotype that can be adjusted for several applications by changing and modifying drug or biomaterial components.
